1. Field of the Invention
The present invention relates generally to automatic transmission for use in automotive vehicles and more specifically to a line pressure control arrangement for such a transmission.
2. Description of the Prior Art
An automatic transmission Service Manual (publication A261C07) issued in March 1987 relating to the so called RE4RO1A type transmission describes an arrangement which utilizes tabled data for controlling the line pressure during shifting and non-shifting modes of transmission operation.
In this arrangement in order to control the level of line pressure to one suited for the instant mode of engine operation and thus obviate shift shock which tends to be induced by excessively high line pressures, the engine throttle valve opening degree is used to determine the duty cycle of a signal which is used to control a line pressure control solenoid valve.
However, with this arrangement, because the amount of torque produced with respect to a given throttle setting tends to vary widely during low throttle setting modes of operation, shift shock still tends be produced.
During attempts to remedy this problem, a less preferred embodiment of the present invention has attempted to use engine torque (as indicated by air flow for example) in place of the throttle valve position parameter. However, with this measure, at high engine speeds with the throttle valve setting in the high zone, during shifting, the effects of inertia are such as to prolong the shifting time and to interfere with the synchronization of the rotational speeds of the input and output shafts of the transmission for the given shift. Accordingly, shift shock tends to be produced and the problem is merely moved from a low throttle setting mode to a high one.